1. Field of the Invention
The present invention relates to methods and devices for minimizing membrane fouling for microfluidic separators. In particular, methods and devices related to minimizing filter cake build-up on a membrane exposed to live oilfield fluids downhole.
2. Background of the Invention
The ability to reliably separate a fluid of interest can be very beneficial for oilfield, medical, biological, and analytical chemistry applications. Fluids of interest may include water, oil, gas, or other fluids. Separating fluids of interest enables specific measurements to be performed on the particular fluid. For example, pH and various ion concentrations may be measured if the fluid of interest is water. For oil, near-infrared absorption spectroscopy may be performed to detect various light-weight hydrocarbons, and other types of chromatography may be used to detect detailed chemical composition.
However, in order to perform accurate measurements on the fluid of interest, the fluid of interest must be separated from other components prior to taking the measurements. A major problem in accomplishing the separation of other components includes fouling or clogging of the separation device. For example, separation methods conventionally used in the oilfield industry can include gravity separation, centrifugation, and hydrocyclone separation. Conventional methods are used to separate large quantities (i.e. for production purposes) and have several drawbacks. One drawback of conventional separation techniques is the time it takes to perform them. Conventional separation techniques often take a long time, depending on the particular composition of the fluid. For example, a fine emulsion may take months to separate by gravity, although a simple mixture may take only a few minutes. Another drawback of conventional separation techniques is poor separation performance. Conventional separation techniques usually do not perform a complete separation. There are almost always traces of contaminants in the sample fluid of interest.
In addition, in most oilfield applications, analyses of formation fluids of interest are typically performed at the surface adjacent to the well or in a remote laboratory environment. However, bringing sample fluids to the surface, transporting them to a laboratory, and separating the phase mixtures is time consuming, cost inefficient and provides only post-factum information. Moreover, fluid samples collected downhole can undergo various reversible and irreversible phase transitions between the point of collection and the point of laboratory analysis as pressure and temperature conditions change.
Recently, biologists and analytical chemists have started to perform analysis of various fluids in laboratories on a micro-scale. The analysis of minute fluid amounts is accomplished with various microfluidic and/or MEM (Micro Electro-Mechanical) systems. Microfluidic systems or devices are typically comprised of fluidic channels with lateral dimensions ranging from tens to hundreds of micrometers and are designed to operate with extremely small volumetric flow rates. However, similar to analysis on a macro-scale, at the micro-scale it is equally necessary to separate the fluid of interest from other fluids in order to perform an effective analysis. Prior to a co-pending patent application Ser. No. 10/885,471 filed Jul. 6, 2004 and entitled “Microfluidic System for Chemical Analysis,” which is hereby incorporated in its entirety by this reference and is assigned to the same assignee of this application, along with another co-pending patent application Ser. No. 10/935,858 filed Sep. 8, 2004 as and entitled “Microfluidic Separator,” which is hereby incorporated in its entirety by this reference and is assigned to the same assignee of this application, microfluidic devices for oilfield applications have only been suitable for use in laboratory environments.
Accordingly, there is a need for a microfluidic separator capable of separating emulsions, liquid-liquid and liquid-gas mixtures in any environment while minimizing fouling of the membrane, fouling can include a filter cake build-up and/or clogging of membrane pores by particulates or other particulates in the fluid, which can include uphole and downhole oilfield environments.